Recently, the demand for a flat display device represented by a liquid crystal display device has been rapidly increasing thanks to its features such as thinness, light weight and low-power consumption. In particular, an active matrix display device which electrically separates an on-pixel and an off-pixel and provides an each pixel with a pixel switch having a function to retain a video signal to an on-pixel is used for a variety of displays such as a mobile information device.
Regarding such a flat active matrix display device, an organic electroluminescent (EL) display device using a self-luminous element has been receiving attention and is being actively researched and developed. An organic EL display device has a feature that it requires no backlight and it is suitable for reproducing a video because of its rapid response capability and also suitable for the use in cold environments because its luminance does not decrease at low temperatures.
Generally, an organic EL display device comprises a plurality of pixels provided side by side in a plurality of rows and in a plurality of columns. Each pixel is constituted by an organic EL element which is a self-luminous element and a pixel circuit which supplies the organic EL element with a drive current, and performs a display operation by controlling the light-emitting luminance of the organic EL element.
In an organic EL display device, there is characteristic variation of a drive transistor provided with a pixel electrode, which causes variation in display luminance and decreases image quality. Therefore, there is proposed an image circuit which includes a circuit for compensating such luminance variation. On the other hand, in an organic EL display device, luminance gradient in which displayed luminance differs in the right and left on a screen occurs in addition to the above-mentioned variation in display luminance.